Measurable Quantities in Sensor Technology

Chapter 2: Sensors and Signal Conditioning

• Sensors are devices that detect and respond to physical phenomena (e.g., temperature, light, motion) and convert them into measurable electrical signals.
• Sensors are critical in various fields such as healthcare, automotive, environmental monitoring, and smart technology.
• Sensors can measure various physical quantities.
• Transducers convert energy from one form to another.
• Transducers are widely used for signal conversion purposes.
• Sensors are a special type of transducer designed primarily for measuring physical quantities.
• Transducers are classified according to their principle usage.

Content Outline

• Introduction
• Transducer vs Sensors
• Transducer Classifications
• Commonly Detectable Phenomena (e.g., temperature, pressure, light, motion, acceleration)
• Measurable quantities (e.g., position, velocity, acceleration, force, pressure, torque)
• Sensor Classifications
• Choosing a Sensor
• Technical Datasheets

Introduction

• Devices that detect and respond to physical phenomena and convert them into measurable electrical signals.
• Critical in various fields, including healthcare, automotive, environmental monitoring, and smart technology.

Sensors Today!

• List of sensors displayed in a diagram (e.g., Camera, Bluetooth, Touchscreen).

Transducers vs. Sensors

• Sensors are designed to measure physical quantities.
• Sensor outputs are usually electrical signals.
• Transducers convert energy from one form to another.
• Transducers focus on energy conversion.

Transducer Classifications

• Principle used (e.g., resistive, capacitive, inductive, piezoelectric)
• Analog/Digital
• Passive/Active
• Primary/Secondary
• Inverse Transducer

Principle Used

• Resistive: Change in resistance based on the measured variable.
• Capacitive: Change in capacitance based on the measured variable.
• Inductive: Change in inductance based on the measured variable.
• Piezoelectric: Electric charge generated due to mechanical stress.

Resistive Transducers

• Principle: Operate based on the change in resistance of a material when a physical quantity is applied.
• How it works: When a physical phenomenon affects the resistive element, the electrical resistance changes. This change can be measured and converted into a corresponding electrical signal.
• Example: Strain gauges (measure deformation), Thermistors, Potentiometer.

Capacitive Transducers

• Principle: Ability of a system to store charge.
• How it Works: Conductive plates separated by an insulating material (dielectric). Physical quantity changes the distance or area between the plates, changing the capacitance. This variation measures as an electrical signal.
• Example: Capacitive sensor (measures changes in capacitance due to displacement or pressure).

Inductive Transducers

• Principle: Operate based on changes in inductance due to variations in magnetic fields or position of conductive objects.
• How it works: Utilize coils of wire generating a magnetic field. When a metallic object approaches the coil, the magnetic field changes and the inductance of the coil changes.
• Example: LVDT (Linear Variable Differential Transformer), Inductive Flow Meters.

Piezoelectric Transducers

• Principle: Certain materials generate an electrical charge in response to mechanical stress or pressure.
• How it works: When mechanical stress is applied to piezoelectric materials, they generate an electrical charge proportional to the stress.
• Example: Piezoelectric sensor, Microphones, Ultrasonic Transducers.

Analog vs. Digital Transducers

• Analog produces a continuous signal (e.g., voltage, current), output smoothly varies over time.
• Digital produces a discrete or binary output, output has distinct steps and does not vary continuously.
• Digital signal easily transmitted over long distances, commonly used in digital systems (like microcontrollers).

Active vs. Passive Transducers

• Active transducers generate their output signal from a physical input without external power.
• Example: Piezoelectric transducer measures pressure or vibrations, generating an electrical charge.
• Passive transducers require an external power source to operate.
• Example: Light Dependent Resistor (LDR) (resistance changes depends on light intensity).

Primary vs. Secondary Transducers

• Primary: Directly converts a physical quantity to an intermediate signal (e.g., mechanical signal).
• Secondary: Converts the primary output signal to a more usable form (e.g., electrical).
• Example: Bourdon tube (converts pressure into mechanical displacement) and LVDT (converts displacement into an electrical signal).

Inverse Transducer

• Device that converts an electrical signal into a physical effect (opposite of a typical transducer).
• Electrical energy converts to physical response.
• Examples: Electric Motors, LED, Piezoelectric Actuator.

Activity 1: Explore the Resistive-type Sensor

• Objectives: Building a simple force sensor using common materials and exploring how external force affects its resistance changes
• Materials: Paper, Pencil, Multimeter, conductive tape, wires, crocodile clips
• Procedure: Described with diagrams (steps for constructing a paper-based force sensor).

Activity 2: Exploring Smartphone Sensors

• Use the Phyphox app to explore various sensors on a smartphone by navigating the Raw Sensors category.
• Procedure: Described for different sensor categories (e.g., Acoustics, Acceleration, Light, Proximity, Magnetometer).

Sensor Classifications

• Mechanical Sensors: Measure quantities like position, velocity, and force.
• Temperature Sensors: Measure temperature or heat.
• Acoustic Sensors: Measure sound and vibrations.
• Optical Sensors: Detect presence of objects.

Activity 3: Guess the Sensor

• Objectives: To identify a randomly assigned sensor and analyze its properties, principle, and applications.
• Procedures: Researching assigned sensor to provide information such as sensor name, measurable quantity, how it works, and applications.

Sensor Classifications

• Potentiometer: Variable resistor based on position of a wiper (used for volume control or position sensing in industrial components).
• Strain Gauges: Measure the amount of strain (deformation) in an object (applied in load sensors, structural health, aerospace & automotive).
• Accelerometer Sensor: Measures acceleration forces. (used in smartphones, automotive stability, and industrial monitoring).
• Tilt Sensor: Measures the angle of inclination (used in automotive, construction, and home automation).
• Thermistor: Resistance varies significantly with temperature (used in temperature measurement and control).
• Infrared Thermal Sensor: Detects and measures temperature based on Infrared radiation (used in medical devices and industrial monitoring to prevent overheating)
• Sound Sensor, Ultrasonic Sensor, Infrared Proximity Sensor, Photogate Sensor.
• Light Dependent Resistor (LDR): Passive electronic component that has resistance that decreases with increasing light intensity (used in automatic lighting, light meters).
• Humidity Sensor: Environmental sensor that measures moisture content in the air (used for weather monitoring, agriculture, and home appliances).
• Soil Moisture Sensor: Measures the moisture content in soil (used in irrigation, agriculture, and greenhouse control).
• Touch Sensor: Input sensor that detects touch and proximity (used in smartphones, tablets, and home appliances).

Choosing a Sensor

• Choosing the appropriate sensor based on application needs (e.g., measurement range, operating environment, accuracy).
• Considering sensor type, specifications, and costs.
• Understanding sensor specifications (operating range, sensitivity, resolution, response time, power requirements, environmental conditions, and cost).

Signal Conditioning

• Functions that prepare sensor signals for processing (e.g., amplification, attenuation, filtering).
• Protecting signals from unwanted effects (e.g., noise, distortion, overvoltage).
• Using analog-to-digital converter (ADC) for digitalization.

Operational Amplifiers (Op-Amps)

• Key configurations of operational amplifiers (e.g., inverting, non-inverting, voltage follower).
• Working principle, circuit diagrams, equations, and applications.
• Analog-to-Digital Conversion (ADC) method that converts analog signals into digital signals; converting the real world (analog) to digital signals in applications (like temperature, pressure, sound, and light) to be processed and analyzed.

Analog-to-Digital Converters (ADC)

• Electronic device that converts continuous analog signals to digital data for processing by computers.
• Important for interfacing the real world (analog) with digital-based systems enabling easy conversion (e.g., temperature, pressure).
• Analog-to-digital processing (ADC) converts physical measurements to computer understandable digital values.

List of References

• Provides links to external resources for further learning.

Test your knowledge about various sensors and their measurable quantities across thermal, acoustic, electromagnetic, and other categories. The quiz covers the use of the Phyphox app and real-world applications of different sensors. How well do you understand the technology behind these measurements?